Extendible Hash File Search

1
Extendible Hash File Search

• Perform Hash function H on key,
  pkey H(key)
• Assign high order D bits of pkey, where D is the
  Directory depth, to i,
  i High_Order(D,pkey)
• Get pointer to leaf page,
  lptr Directoryi
• Search page pointed to by lptr for record with
  key
• If found record in step 4 then return record else
  return Not Found

2
Extendible Hash File Insert

• Perform steps 1 thru 3 from Search algorithm
• Access page pointed to by lptr
• If there is room for another record on that page
• Then store the new record there
• Else
• Begin
• get space for new leaf page,
  new_lptr is pointer
• to new leaf page
• increase depth of leaf page by 1
• set depth of new leaf page to be
  the same as
• that for page pointed to by
  lptr
• divide records between the two
  leaf pages pointed to by lptr
• and new_lptr

3

• Extendible Hash File Insert (continued)
• If new pages depth is gt Directory
  depth Then
• Begin
• increase directory depth by
  1
• double directory size
• update pointers in directory
  
• End
• Else
• update directory so that it
  points to new_lptr page
• If could not insert new record
• Then repeat Insert Algorithm from
  step 1
• End

4
Linear Hash File Search

• bucket key MOD (2Level N)
• If bucket lt next
  
  
  Then bucket
  key MOD (2Level1 N)
• Search bucket for record with key (may involve
  searching overflow for bucket)
• If found record then return record else return
  Not Found

5
Linear Hash File Insert

• Perform steps 1 and 2 of Search Algorithm
• Access bucket found in step 1
• If room available in bucket
• Then insert new record
• Else If overflow buckets
• Then
• Begin
• search for room in
  overflow
• If room Then
  insert
• Else add another
  overflow bucket with new record
• End
• Else add first overflow bucket
  with new record

6
Linear Hash File Expand

• Expand bucket and its overflow chain at location
  next,
• add new bucket at location next
  (2Level N)
• to distribute records from bucket next
  and the new bucket, use key MOD (2Level1 N)
• next (next 1) MOD (2Level N)
• If next 0 Then level level 1